1. Field of the Invention
This invention pertains generally to a means for connecting a vacuum pump to a chamber to be evacuated and pertains particularly to such a connecting means which also provides a pumping action by having the specific feature of a gas sorbing material on the inner surface of the connecting means.
2. Description of the Prior Art
It is often desirable or necessary to produce a region of substantially reduced pressure or a vacuum within an enclosed space or volume. Many different methods have been proposed to produce this desired vacuum. One method in wide spread use is by means of mechanical pumps which operate by trapping gas molecules or atoms from the vessel in which it is desired to produce the vacuum. These trapped molecules or atoms are then mechanically transferred to a region of higher pressure outside the vessel. Many types of mechanical pump are known such as the rotary pump which has many variations. However these pumps are generally not capable of producing vacuua less than about 10.sup.-2 torr or about 10.sup.-4 torr when two are placed in series. They also have difficulty in pumping the gases which are easy to condense such as water vapor and additional techniques have to be used such as the addition of a gas ballast or air leak. Such mechanical pumps, while capable of removing large quantities of gases at high speeds, are not capable of reaching the low pressure which are presently required. In order to reach lower pressures mercury or oil diffusion pumps have been used. These pumps operate by providing a high speed jet of mercury or oil of lower vapor pressure. The jet or steam of mercury or oil entraps molecules or atoms of gas, which diffuse from the volume or chamber to be pumped, and remove them to a region of higher pressure. Usually the diffusion pump is aided by means of a backing pump which generally consists of a mechanical pump such as those already described. Practical considerations usually limit the lower pressure reached with these diffusion pumps to about 10.sup.-8 torr, although techniques are known by which these pumps can give better vacuua.
Many other types of pumps are known for producing vacuua such as those which operate by the evaporation of a metal, which is then capable of reacting with gas molecules or which buries them under the surface of the evaporated metal. Such pumps however can be unstable when pumping rare gases such as He, Ne, Ar, etc. and may not even pump them at all.
The so called turbo-molecular pump has also gained great favor in the production of high vacuua but its performance with respect to hydrogen is not as good as for other gases of higher atomic or molecular weight.
Very often a combination of different types of pumps is used to try and attain a more even removal of all species of gas from the chamber to be evacuated. Unfortunately the various combinations have not lead to the attainment of the extremely low partial pressure levels of all residual gases which are now known to be required in certain vacuum chambers.
The connection means between the pump and the chamber can also be a source of gas which may limit the lowest pressure attainable in the chamber.
Heating process are used to aid in reducing the quantity of gas remaining upon or within surfaces which could later be released and decrease the quality of the vacuum. It is also known to use a gas sorbing means or trap placed between the vacuum pump and the chamber however this trap is usually in the form of a separate device placed between the pump and the chamber still leaving an undesirable connection means between the trap and the chamber. The trap may be electrical in nature or consist of cooled surfaces and zeolites. Sometimes it is necessary to use cryogenic techniques which require additional ancilliary equipment.
It is therefore an object of the present invention to provide a means for connecting a vacuum pump to a chamber to be evacuated which is substantially free from one or more of the disadvantages of prior connecting means.
A further object is to provide a means for connecting a vacuum pump to a chamber required to be evacuated which also provides a pumping action.
Another object is to provide a vacuum pumping system in which there is an improved connection means between the vacuum pump and the chamber to be evacuated.
Yet another object of the present invention is to provide an improved method of pumping a chamber to sub-atmospheric pressures.